You know, I always assumed that meant two separately processed reverbs, each one based on, say, HALL. But I’m not so sure any more. Identical A & B side settings seem to have subtle differences. One side has more early reflections & bloom? Depending on various MIX and SIZE values, I hear elements of ROOM, PLATE; sometimes that random modulation of allpass filters from the ‘big’ algorithms.
I tossed together a quick preset as a testing ground. While the crossed AB-MIX values sound luscious, DUAL-MONO is perfect to separate what’s happening on each side. I ‘ping-ponged’ the A/B-PREDELAYs to enhance that. Now just tweak around with the MIXes, SIZE, A-B-TONE …
The expression pedal mapping serves two purposes. It’s an easy way to dial up the two DECAY times simultaneously, then audition. It also tops out at FREEZE, where many of the parameters still stay ‘active’.
I think RESONANCE here is just that: a variable peak at the area surrounding the corner frequency. Speculating, but perhaps shelving at familiar points: 350 Hz. & 2000 Hz. If you use the EXP PED to FREEZE, you can hear it’s effects while you dial RESONANCE CCW / CW, or adjust the A-TONE & B-TONE. Just hold for 900 mS before you snap to FREEZE, so you capture both the A&B sides.
As for the OUTPUT level discrepancies, I wouldn’t know. It may be the only algorithm with completely independent signal paths. When you cram all this controls into two reverbs, maybe you need every cycle you can spare. Interesting discussion. This is an unfairly neglected algorithm, on my part.